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Determination of potential reactivity of MSWI fly ashes in cementitious materials Thibault LENORMAND1, Aurore DE BOOM2, Marc DEGREZ2, Christian PIERRE3, Stéphanie STAQUET1
1: Université Libre de Bruxelles, BATir 2: Université Libre de Bruxelles, CREA-SURF 3: CRIC-OCCN Conference WASCON 2012, 31-05-2012 Gothenburg, Sweden
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Contents
• Introduction
• Materials and methods
• Results
• Conclusion
2
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• What to do with a solid containing….?
Introduction
3
CaO SiO2
Al2O3 Fe2O3
It looks cement,
doesn’t it?
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• but also…
Introduction
4
CaO SiO2
Al2O3 Fe2O3
NaCl KCl
ZnO PbO
…
A salty cement…
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• “Just” remove chlorides and heavy metals!
Introduction
5
CaO SiO2
Al2O3 Fe2O3
NaCl KCl
ZnO PbO
…
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• How?
Introduction
6
CaO SiO2
Al2O3 Fe2O3
NaCl KCl
ZnO PbO
…
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Introduction
• Municipal Solid Waste Incinerator (MSWI) fly ashes – Hazardous materials
• Currently landfilled
• Different problems
– Environmental problems
– Shortage of place
– Lack of natural materials
• Goal of this research – Use MSWI fly ashes in cementitious materials as mineral addition
• In partial replacement of cement
7
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Introduction
• Treatment methodology
8
Treatment
Incorporation in
cementitious
materials
Modifications to
apply to the
treatment
Validation of
treatment
modifications
Treatment validation
Bibliographic
study
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Materials and methods
• Replacement of a part of cement CEM I 52.5N by MSWI fly ashes
• Ratio Water/Binder = 0.5 – Binder : cement + MSWI fly ashes
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Cement
MSWI fly ashes
Cement
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Materials and methods
• Characterisation methods
Compressive strength
Calorimetric analyses
Setting time
Gravimetric measurements
10
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Materials and methods
• Compressive strength
– According to EN 196-1 standard
– Carried out on mortars prims 4*4*16 cm3
• Calorimetric analyses
– Isothermal measurement at 20°C
– Carried out on cement paste samples
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Methods - Compressive strength - Heat flow - Setting time - Volume
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Materials and methods
• Setting time measurement
– Determined by ultrasounds velocity
measurement
• With FreshCon device
– Carried out on mortar or cement paste
12
0
500
1000
1500
2000
2500
3000
0 5 10 15 20
Ult
raso
un
ds
velo
city
(m
/s)
Time (hour)
Initial setting
Final setting
Step 1 : Fresh mortar or cement
paste
Step 2 : Hardening of material,
acceleration of ultrasounds
Step 3 : Hardened material
Methods - Compressive strength - Heat flow - Setting time - Volume
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Materials and methods
• Gravimetric measurement – Determination of volumetric variations of a cement paste sample
according to Archimedes' principle
– Cement paste was put in an elastic waterproof membrane
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Thermo-
statically
controlled
water bath
Scale
Data-gathering
system
Cement paste
sample
water
membrane
MV
Methods - Compressive strength - Heat flow - Setting time - Volume
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• MSWI fly ashes ONLY from the electrostatic precipitator
Materials and methods
14
CaO SiO2
Al2O3 Fe2O3
NaCl KCl
ZnO PbO
…
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Results
• Water treatment to reduce chloride quantity – Washing with distilled water
• Ratio Liquid/Solid = 5
• 1 hour
• Use of water treated MSWI fly ashes (notation WT) – As replacement of cement
• 12.5%
• 25%
• 37.5%
– Reference :
• Without cement substitution
15
Effects on - Compressive strength - Heat flow - Setting time - Volume
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Results
• Compressive strength
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0
10
20
30
40
50
60
70
80
0 20 40 60 80 100Co
mp
ress
ive
str
en
gth
(M
Pa)
Time (day)
Reference WT 12.5
WT 25 WT 37.5
Important decrease of compressive strength with the increase of WT MSWI fly ashes
Different explanations → Diminution of cement quantity → Anhydrite Ettringite → Oxidation of metallic aluminium
→ Emission of hydrogen → Creation of bubbles and crackings
222 32222 HAlOOHOHAl
Mortar prism WT 37.5
Water treatment effects on - Compressive strength - Heat flow - Setting time - Volume
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0
0.5
1
1.5
2
2.5
3
3.5
0 1 2 3 4 5 6 7
No
rmal
ize
d h
eat
flo
w
(mW
/g)
Time (day)
Reference
WT 12.5
WT 25
WT 37.5
Results
• Hydration – Heat flow
• Setting time
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3.1 4.512.4 16.2
38.944.5
85.792.7
0
20
40
60
80
100
Initial setting Final setting
Tim
e (
ho
ur)
Reference WT 12.5 WT 25 WT 37.5
Important delay in hydration and setting time → Impact of heavy metals (Pb, Zn), known as setting retarders
Water treatment effects on - Compressive strength - Heat flow - Setting time - Volume
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Results
• Volume
18
Treatment with water → Swelling of cement paste membrane → Not efficient to oxidize metallic aluminium
90%
100%
110%
120%
130%
140%
150%
0 20 40 60 80 100
Vo
lum
e (
%)
t (h)
ReferenceWater treatment
142%
97.3%
Water treatment effects on - Compressive strength - Heat flow - Setting time - Volume
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Results
• Water treatment
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Decrease in compressive strength → Oxidation of metallic aluminium → Emission of hydrogen in cementitious materials
Important delay in hydration → Heavy metal concentration (Pb, Zn)
→ Oxidize metallic aluminium during the treatment step
→ Heavy metal concentration to be decreased
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Results
• Decrease in heavy metal concentration
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Separation of MSWI fly ashes in 3 fractions :
• < 38 µm • 38 – 90 µm • > 90 µm
→ Increase in heavy metals concentration with the decrease in fraction size → Setting times were measured for each fraction
• Incorporation rate of 25%
3.1 4.5
44.9 50.2
41.847.9
15.0 17.8
0
10
20
30
40
50
60
Initial setting Final setting
Tim
e (
ho
ur)
Reference WT F90 25
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Results
• Oxidation of metallic aluminium
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Treatment with sodium hydroxide → Shrinkage of cement paste membrane
→ Efficient to oxidize metallic aluminium
97.0%
97.5%
98.0%
98.5%
99.0%
99.5%
100.0%
0 5 10 15 20 25 30
Vo
lum
e (
%)
t (h)
ReferenceBasic treatment
99.3%
97.3%
→ Treatment with sodium hydroxide selected
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Results
• New treatment
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3.1 4.57.3 9.8
38.944.5
15.0 17.8
0
10
20
30
40
50
60
Initial setting Final setting
Tim
e (
ho
ur)
Reference BT 25 WT 25 WT F>90 25
Combining size-based separation and basic treatment → Water washing to remove chlorides → Selection of the less contaminated fraction → Oxidation of metallic aluminium during treatment step
BT: Basic treatment combining water WT: Water treatment WT F>90: Water treatment and selection of the fraction upper 90 µm
Basic treatment • Setting times were the less delayed • Delays were reduced compared
with WT 25
No damage was observed because of hydrogen emission
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Conclusion
• Raw MSWI fly ashes have to be treated before their incorporation in cementitious materials – Water washing to remove chloride
– Size-based separation to decrease heavy metals concentration
– Basic treatment to oxidize metallic aluminium
• After this treatment – Use of treated MSWI fly ashes in cementitious materials without
damage
– Further study of the reactivity of treated MSWI fly ashes in cementitious materials
• Carried out currently
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Thank you for your attention